Split strap supporting means for electrical insulators



Jan. 9, 1962 A.'w. HACKMAN ET AL 3,016,441

SPLIT STRAP SUPPORTING MEANS FOR ELECTRICAL INSULATORS Filed May 23,1960 2 Sheets-Sheet 1 O o o O z 25 74 w or J f 27 74 22 e22 035' 76 76012205 W Haze/ man [749 f 011/ lift/06026022 Jan. 9, 1962 A. w. HACKMANET AL 3,016,441

SPLIT STRAP SUPPORTING MEANS FOR ELECTRICAL INSULATORS Filed May 23,1960 2 Sheets-Sheet 2 (Z722 0,9 ZZZ ifiac/fman ifi'fora' fl Jacobsozzll/17 @(s e a United States Patent f 3,016,441 SPLIT STRAP SUPPORTINGMEANS FOR ELECTRICAL INSULATORS Amos W. Hackman, Kirkland, and ClilfordH. Jacobson,

Kingston, 111., assignors to Tuttle Electric Products,

Inc., Kirkland, 11]., a corporation of Illinois Filed May 23, 1960, Ser.No. 31,040 7 Claims. (Cl. 219--19) This invention is directed to the artof open coil heaters embodying a heating resistance of substantiallength which is exposed to an area being heated and particularly relatesto improvements in supporting and insulating assemblies for the coils ofthese heaters. The coils of these heaters, which are commonly used 1nappliances of conductive material, such as clothes dryers, are usuallysupported by metallic frames which must be electrically insulated fromthe coils. The insulators which are used must support the coil in suchfashion that they do not cause hot spots or overheating of the coil atplaces of support thereof, as such hot spots may result in theresistance burning out. Furthermore, excessive heating of the insulatorssometimes causes the insulator to acquire surface conductivity so thatthere may be some surface creepage of current along the insulator, whichis passed through the metallic support and the article used with theheater, thereby offering dangerous shock possibilities to the attendantor operator coming in contact with the article or machine with which thecoils are used.

The present invention aims to minimize such hot spots in the coil ofthese heaters, thereby minimizing the tendency for the coil to burn outand minimizing the surface creepage of current aforementioned, byproviding an insulating and supporting assembly that is so formed as toprovide for a minimum of contact between the insulator and the support,and greater exposure of the insulator surface for dissipation of heattherefrom and also provide simplicity, convenience and economy in theassembly of the insulators and parts by which they are supported.

The principal objects of the invention are to provide improved open coilmetal frame heaters of the type referred to; to provide an improvedinsulating support for open coil heaters; to facilitate the fastening ofsupports for insulators of open coil heaters to a supporting member; toform an insulating assembly for such heaters in a manner minimizingoverheating of the coil, or hot spots, and also surface creepage ofcurrent at the places of insulated support thereof; these and otherobjects being accomplished as described more particularly hereinafterand as shown in the accompanying drawings in which:

FIG. 1 is a plan view of an open coil heater embodying the presentinvention;

FIG. 2 is an enlarged sectional view of a portion of the heaterillustrated in FIG. 1, taken on the section line 22, of FIG. 1, andparticularly illustrating one form of insulating support for a pair ofcoils;

FIG. 3 is a view taken on the line 33 of FIG. 2 and particularlyillustrating the relation of an insulator to its supporting strap;

FIG. 4 is a plan view of a supporting strap, with portion broken away,used with the assembly illustrated in FIGS. 2 and 3;

FIG. 5 is a view of one end portion of a supporting strap similar tothat of FIG. 4 but showing a modification thereof for fastening thereofto a companion strap;

FIG. 6 is an edge view of the strap portion of FIG. 5 showing thefastening tongue thereof bent outwardly therefrom;

FIG. 7 is a side view of a fragmentary portion of an insulator showingthe fastening of companion straps thereon with the tongue fastener ofFIGS. 5 and 6;

FIG. 8 is a plan view of a single strap which may be used for supportinga pair of insulators.

FIG. 9 shows a side view of a pair of insulators supported by the strapof FIG. 8;

FIG. 10 shows a single insulator modification of the mounting shown inFIG. 9;

FIG. 11 shows another form of single insulator mount- FIG. 12 is asectional view taken on the line 1212 of FIG. 11;

FIG. 13 is a side view of another form of single insulator mounting;

FIG. 14 is a side view of another plural insulator mounting which isapplicable to a series of insulators;

FIG. 15 is a top view of the strap assembly of FIG. 14;

FIG. 16 is an assembly view of a heater support utilizing the principlesof the invention as applied to a curvilinear supporting frame member;and

FIG. 17 illustrates a modified form of embrasure of the insulator by thedivided portions of the strap.

With particular reference now to the drawings, and in the first instanceto FIG. 1, the reference numeral 20 designates a supporting frame as awhole for coils 21 and 22 of an open coil resistance heating assembly.The frame 20 may include a pair of elongated metallic strips 23 whichare rigidly secured at their opposite ends to transversely extendingopposite end strips 25 and 26 respectively to provide laterally spacedsupporting elements on which holders are mounted by which the coils ofthe heating resistance are supported.

One coil 21 may be longer than the other and supported as an outer coilon the frame, as shown herein, whereas the other coil 22 may be disposedinwardly of the outer coil and in the general position as illustrated inthe drawings. It should be understood that the general disposition ofthe coils 21 and 22 is merely illustrative and other arrangementsthereof may be employed. The ends of the coils 21 and 22 lead toterminals 74 which are mounted in insulators extending through aterminal plate 27 which is attached to the frame 20.

In using this class of heater it is important to provide as much exposedarea of the convolutions of the coil as possible for maximum heattransferring effect between the heating coils and the area or spacebeing heated.

In accordance with the present invention the coils are supported atspaced intervals along their lengths by ceramic insulating bodies 28.These insulators have a generally tubular or cylindrical form, as isseen in FIGS. 1 and 3, and include an externally formed rib 29 extendingcircumferentially about the insulator near the center thereof by whichthe insulator is locked in encircling strap means, said rib alsoproviding extra surface for dissipation of heat. These insulators havean open passage formed therein and extending longitudinally therethroughand this passage is preferably formed with opposite end portions ofsubstantial length defined by outwardly flared or beveled encirclingsurfaces 30 with a narrow coil supporting surface 31 therebetween whichis of a diameter to loosely support the coil and hold it out of contactwith the flared or beveled surfaces 30. Surface 31 may have a width(taken longitudinally of the insulator) approximately the width of therib 29 so that the thickest wall portion of the insulator occursgenerally at the central portion thereof. Surface 31 accounts for only aminor portion of the length of the passage through the insulator and theflared portions 30' which are out of contact with the coil providerelatively long distances between the surface 31 and the ends of theinsulator.

When supporting the insulators from the framework it is important tosupport them in such fashion that heat, which is transferred to theinsulators during energization of the coils, is dissipated asefficiently as possible. The insulators are supported from the frameworkby supporting members or insulator holders designated generally at 32,and which surround the external annular surface of the insulators so asto loosely confine the insulator in the supporting members. Eachsupporting member is formed with laterally spaced relatively narrowportions 33 and 34 which conform to and engage the periphery of theinsulator at opposite sides respectively of the rib 29, and theseportions 33 and 34 may be applied flatwise around the insulator ends asshown in FIGS. 2 and 3 or may be turned up on edge as indicated 76 inFIG. 17 for edgewise contact with the insulator.

The supporting members 32 preferably are lengths of metallic strap stockwhich are split or divided longitudinally to provide narrow portions 33and 34 separated by a slot 35 to receive the insulator rib 29therebetween and in the structure of FIGS. 2 and 3 the supporting member32 is made of a pair of split straps 37 and 38 such as shown in PEG. 4,each of which is split at longitudinally spaced places to provide ateach plate a pair of laterally spaced portions 33 and 34 which areseparated by a slot 35 and are correspondingly bent semicircularly tocooperate with the oppositely bent semi-circular portions 33 and 34 ofthe other strap and conjointly embrace the insulator 28 therebetween, asshown in FIGS. 2 and 3.

Each strap has a short end portion 39 at each end thereof beyond theouter ends respectively of the slots 35, each of which said end portionsis bent outwardly for face to face engagement with the corresponding endportion 39 of the other strap and these end portions are securedtogether in such face to face relation, as shown in FIG. 2, as forexample by welding, to fasten the straps around the insulators with theinsulator ribs 29 in the slots 35 of the straps 37 and 38.

Suitable portions of the lengths of the straps 37 and 38 are providedbetween the respective slots 35 thereof and shaped in conformity withone another to mate with one another in face to face relation to providea composite bridging 40 between the insulator holding semicircularportions thereof and are conjointly secured at their midlength to themembers 23 of the, supporting frame, as by a rivet 42 as in FIG. 2 inwhich the holder 32 is shown as attached to the strip 23.

The composite bridging 40 preferably extends outwardly beyond the strip23 at opposite sides thereof as shown in FIG. 2 and is bent upwardly asshown to hold the insulators 28 in an offset position at one side of thestrip 23 or 24, and the slots 35 extend sufficiently into the outer endsof the upturned portions of the bridging and also into the securedtogether ends 39 of the straps to provide clearance as shown at 36 tostraddle the ribs 29.

It is to be noted, particularly in FIG. 3, that the side portions 33 and34 are relatively narrow and extend over a very narrow portion of thelengths of the insulator at opposite sides of the rib and leave theentire rib and most of the length of the insulator at opposite sides ofthe rib exposed for free access of air to the insulator surface forrapid dissipation of heat from the insulator, and to increase thesurface exposure of the insulator to free access of air thereto theportions 33 and 34 may be arranged for edgewise engagement with theinsulator by turning the portions 33 and 34 outwardly, for example asshown at 33 and 34 in FIG. 17.

The straps may be formed with integral tongues for fastening the twoparts 37 and 38 together, or for making up insulator holders of otherforms and bracing thereof on the strips 23 as hereinafter explained,such 4 tongue fastening for the straps 37 and 38 being shown in FIG. 7.

For the tongue fastening of FIG. 7 the straps 37 and 38, the stockbetween the side portions 33 and 34 of one of the straps, for examplethe strap 38, is not entirely removed, but instead a tongue portion 41is left therebetween at the outer end of each slot 35, as shown in FIG.5, which may be bent laterally therefrom, as indicated at 41 in FIG. 6,and this tongue 41 is passed through the slot 35 of the other strap 37at the outer end of the slot and bent outwardly over the end tab portion39 of the strap 37, as shown at 41 in FIG. 7, to secure the straps 37and 38 together at their outer ends around the insulators 28 in lieu ofwelding the strap ends together.

FIG. 9 illustrates another embodiment of the invention in which thesuppoiting member for a pair of insulators 28 is formed from a singlesplit strap 43 such,

as shown in FIG. 8. This single strap 43 is similar to the straps 37 and38 of the FIG. 2 construction except that it has slots 44 and narrowportions 45 at opposite sides of the slots which are approximately twicethe length of the slots 35 and side portions 33, 34 of the FIG. 2construction so as to extend entirely around the insulators 28, and theslots 44 are provided with tongues 46 of the strap stock at the innerends of the slots 44. At their outer ends the slots 44 have tab ends 47of the strap extending therebeyond.

The portion of the strap 43 between the inner ends of the slots 44 issecured centrally to one of the strips 23, as by a rivet 48, and hasarm'portions 49 extending divergently upward at the outer ends of whichthe portions 45 at opposite sides of the slot 44 are bent into circularform, as indicated in FIG. 9, to encircle the insulators 28 and straddlethe rib 29 thereof.

For locking the portions 44 in the insulator confining circular form,the tab is bent radially from the circularly formed portions 45, asindicated in FIG. 9, and the tongue 46 is passed downwardly through theslot 44 at the tab end thereof and bent back underneath the tab and therespective divergent arm 49 to clamp the tab '47 against the arm 49, asshown in FIG. 2, and the tongues 46 may have end portions thereof bentdownwardly against the opposite edges of the strip 23, as indicated at50 to prevent twisting of the insulator supporting member on the strip23.

The principles of the invention may also be applied to a singleinsulator supporting member, one form of which is shown in FIG. 10, inwhich a strap is formed at one end with a foot portion 51 for securementby a rivet 52 to a frame strip 23 or any other appropriate supporttherefor, and has an arm 53 extending angularly upward therefrom andprovided with an insulator holding loop 54 at the outer end thereof.

The loop forming portion of the strap of FIG. 10 is slotted throughoutits length, as in the FIG. 9 structure to accommodate therein the rib 29of an insulator 28 and provide opposite side portions similar to theside portions 45 of FIG. 8 to encircle the insulator at opposite sidesof the insulator rib 29, the strip being provided at the outer end withan end tab portion 55 and a tongue 56 like the end tab 39 and tongue 41of FIG. 5. The outer end portion of the strap of FIG. 10 is bent to lieunderneath the angular arm 53 and the tongue 56 is passed through theslot at the inner end of the latter and folded down against the armportion 53, as shown in FIG. 10, to secure the loop around theinsulator.

The foot portion 51 may be provided with an end portion 57 whichprojects beyond the lateral edge of the Supporting strip and is bentdownwardly thereagainst, as shown in FIG. 10, to prevent twisting of theinsulator supporting member on the strip 23.

In the event that the supporting member is of undue width or it isotherwise inappropriate to hold the supporting member against twistingin the manner illustrated in FIG. 13, as for example when the supportmember is mounted on a Wide strap or plate, such as indicated at 58 inFIGS. 11 and 12, the foot portion 51 may be provided at its end with anarrow downturned tongue and the strap or plate 58 provided with anaperture 60 into which the tongue 59 projects.

It is important that the support surround a su-tficient peripheraldistance of the insulator to adequately hold the insulator in theintended position. The straps may surround substantially the entireperiphery as is illustrated in FIGS. 2, 9 and 10, or may, as illustratedin FIG. 13, surround only a major portion of the periphery therebyleaving a minor portion of the insulator completely exposed. In FIG. 13a single strap 61 includes a medial portion 62 which is bent into aconfiguration conforming generally to the size and configuration of theinsulator. The remaining ends of the strap may be bent away from thecircular configuration thereof as indicated by the portions 63 and 64and then bent at right angles thereto, as at 65 and 66, so that theportions 65 and 66 overlap. The overlapped ends may be secured to asupporting frame member 67 as by means of a rivet 68 and the strap 66may extend beyond the frame member and be bent downwardly, as at 69, soas to bear against the side surface of the frame member 67, therebypreventing turning movement of the strap on the frame member.

FIGS. 14 and 15 illustrate a further embodiment of the invention inwhich two or more insulators 28 may be mounted between straps inlaterally spaced relation.

In this construction of FIGS. 14 and 15 two straps 70 and 71 areemployed which are alike in the respect that each has correspondinglyspaced apart semi-circular portions 72 to mate with the semi-circularportions of the other strap to confine the insulators therebetween, eachof said semi-circular portions being slotted, as at 73, and providedwith opposite side portions 76 for engagement with the interposedinsulator in the same manner as the opposed semi-circular portions 34 ofFIG. 2 engage the insulators 28 for securing the insulatorstherebetween.

The straps 70 and 71 may be secured together in any desired manner, asfor example by spot welding between the semi-circular portions thereof,but in accordance with the present invention it is preferable to fastenthe straps 70 and 71 together with tongues formed from the strip stocksuch as employed in previously described embodiments of the invention.

Thus, as shown in FIGS. 14 and 15, one of the straps, for example, thestrap 71 may be provided at one or both ends of its slots 73 withtongues 77' which are bent through the slots 73 of the other strap 70and folded back over the portions of the strap between the slotsthereof, as shown in FIGS. 14 and 15, and of course, if desired, some ofthe tongues 77 may be provided on one strap and the other tongues on theother strap so that the straps are alike as to the tongues, one havingtongues at one side of each insulator and the other strap having tonguesat the other side of each insulator, for fastening the straps together.

Each of the insulating assemblies shown and described herein providerelatively large heat dissipating exposed surface areas with relativelyshort insulators of tubular form. Each insulator provides a relativelysmall coil supporting area internally thereof with an exposed externalrib positioned radially from the supporting area. Since heat will tendto build up most quickly in the coil supporting area, the use of theexposed rib in this position promotes heat transfer from the coilsupporting region.

The split straps used in each assembly cooperate with the ribs of theinsulators in holding the insulators against displacement and at thesame time provide for maintaining the entire circumference of the ribexposed for effective heat transfer therefrom. In this connection itshould be noted that the ends of the slots between the split portions ofthe straps are spaced from the periphery of the insulator ribs so as topromote air circulation and heat transfer.

By using the relatively narrow portions formed from the same material,the split portions are not only held together for strength in supportingthe insulators, but also facilitate fastening of the straps, as by theuse of the folded tongues of FIGS. 7, 9, 10 and 14.

The insulating supports shown and described herein lend themselves toany shape of coil and any shape of supporting framework. In FIG. 16, forexample, a pair of supporting members of the form illustrated in FIG. 2are shown affixed to a curvilinear supporting frame member 78 with thestrap supports extending generally radially with respect to the centerof curvature of the frame member 78. The supporting framework may beformed into any desired shape or configuration and by using theindividual supports herein shown and described, the coil will bepositioned in a general pattern conforming to the general shape definedby the supporting framework.

While I have shown and described my invention in a preferred form, I amaware that various changes and modifications may be made therein withoutdeparting from the principles of the invention, the scope of which is tobe determined by the appended claims.

What is claimed is:

1. An insulating support for elongated resistance coils of open coilheaters including a generally cylindrical insulating body having acentral passage extending therethrough to provide for a relatively loosesupport of an elongated resistance coil of the open coil heater type,said insulating body having an externally formed heat dissipating ribextending circumferentially thereof adjacent the center thereof, and ametallic support for said insulating body, said support includinglaterally spaced relatively narrow portions passed around and conformingclosely to the external surface of said insulating body, said portionsbeing spaced on opposite sides of the rib of said body, said supportincluding an offset attaching and securing arm, and said spaced portionsbeing passed around a substantial distance of the periphery of saidinsulating body, the metallic support being a split strap with the splitportions of the strap providing the said narrow portions and said straphaving a securing tongue formed from the material of the strap betweenthe split portions thereof at one end of the opening between said splitportions and passed through the other end of the opening in the strapand folded over the body of the strap to secure the body to the strap.

2. An insulating support for elongated resistance coils of open coilheaters including a generally cylindrical insulating body having acentral passage extending therethrough to provide for arelatively loosesupport of an elongated resistance coil of the open coil heater type,said insulating body having an externally formed heat dissipating ribextending circumferentially thereof adjacent the center thereof, and ametallic support for said insulating body, said support includinglaterally spaced relatively narrow portions passed around and conformingclosely to the external surface of said insulating body, said portionsbeing spaced on opposite sides of the rib of said body, said supportincluding an offset attaching and securing arm, and said spaced portionsbeing passed around a substantial distance of the periphery of saidinsulating body, said support being a pair of straps having curvedportions cooperatively embracing the wall of said insulating body, saidstraps being split to provide said narrow portions, one end of eachstrap being offset to provide an attaching arm portion, the other end ofeach said strap being offset, one strap having a tongue bent from thematerial of the strap between said split portions and passed through theopening in the strap adjacent said second-named offset portion andfolded thereagainst so as to secure the strap to the insulating body.

3. An open coil electric heater comprising an elongated electricallyenergizable resistance coil having thereon a plurality of generallytubular electrical insulators through which the resistance coil extends,the insulators being spaced apart along the resistance coil withsubstantial portions of the length of the coil extending openly betweenthe insulators, and electrically conductive coil supportlng means havingelectrically conductive loops through which the coil extends with thespaced apart insulators thereon extending through and secured in theloops and electrically insulating the coil from the supporting means andthe loops thereof, each loop having arcuate opposite side portionsbetween which an insulator is interposed and each arcuate opposite sideportion having a pair of laterally spaced correspondingly arcuategenerally parallel strips defining therebetween a slot at one end ofwhich the strips are outturned and interconnected and secured tointerconnected ends of the strips of the other arcuate opposite sideportion to confine the insulator between the arcuate opposite sideportions, and the insulator being formed substantially centrally betweenthe ends thereof with outwardly projecting portions therearound whichproject into the slots of both said arcuate portions.

4. An open coil electric heater as defined in claim 3 in which theoutturned ends of each pair of strips have the slot ends therebetweenand are in registering relation to one another.

5. An open coil electric heater comprising an elongated electricallyenergiZab-le resistance coil having thereon a plurality of generallytubular electrical insulators through which the resistance coil extends,the insulators being spaced apart along the resistance coil withsubstantial portions of the length of the coil extending openly betweenthe insulators, and electrically conductive coil supporting means havingelectrically conductive loops through which the coil extends with thespaced apart insulators thereon extending through and secured in theloops and electrically insulating the coil from the supporting means andthe loops thereof, each loop having arcuate opposite side portionsbetween which an insulator is interposed and each arcuate opposite sideportion having a slot therein with a tongue at the end of the slot ofone of the arcuate portions extending into the end of the slot of theother arcuate portion and providing a fastening of the arcuate portionsto one another by which the insulator is secured therebetween.

6. An open coil electric heater comprising an elongated electricallyenergizable resistance coil having thereon a plurality of generallytubular electrical insulators through which the resistance coil extends,the insulators being spaced apart along the resistance coil withsubstantial portions of the length of the coil extending openly betweenthe insulators, and electrically conductive coil supporting means havingelectrically conductive loops through which the coil extends with thespaced apart insulators thereon extending through and secured in theloops and electrically insulating the coil from the supporting means andthe loops thereof, each loop having arcuate opposite side portionsbetween which an insulator is interposed and each arcuate opposite sideportion having a pair of laterally spaced correspondingly arcuategenerally parallel strips defining therebetween a slot at one end ofwhich the strips are outturned and interconnected to close the end ofthe slot, the slot of one of the arcuate portions having a tongue at theclosed end thereof extending through the slot of the other arcuateportion and [folded over the closed end thereof to fasten the arcuateportions together at the closed ends of their slots and confine theinsulator therebetween.

7. An open coil electric heater comprising an elongated electricallyenergizable resistance coil halving thereon a plurality of generallytubular electrical insulators through which the resistance coil extends,the insulators being spaced apart along the resistance coil withsubstantial portions of the length of the coil extending openly betweenthe insulators, and electrically conductive coil supporting means havingelectrically conductive loops through which the coil extends with thespaced apart insulators thereon extending through and secured in theloops and electrically insulating the coil from the supporting means andthe loops thereof, said loops being formed of elongated metal stripsshaped to provide loops with opposite arcuate side portions betweenwhich an insulator is interposed, each arcuate side portion having aslot extending throughout the length of the arcuate side portion and theslot of one arcuate side portion having a closed end with a tongue atthe closed end, and the slot of the opposite arcuate side portion havinga closed end through which said tongue extends and is folded overtherebeyond to fasten the opposed arcuate opposite sides together andclamp the insulator therebetween.

References Cited in the file of this patent UNITED STATES PATENTS1,165,451 Ruckle Dec. 28, 1915 1,827,508 Cope Oct. 13, 1931 2,457,608Shafter Dec. 28, 1948 2,752,476 Norris June 26, 1956 2,921,172 Hackma-nJan. 12, 1960 OTHER REFERENCES Publication, Electronic Engineering,August 1958, page 168.

